UPTAKE AND CLEARANCE OF EDWARDSIELLA-ICTALURI IN THE PERIPHERAL-BLOODOF CHANNEL CATFISH ICTALURUS-PUNCTATUS FINGERLINGS DURING IMMERSION CHALLENGE

Uptake and clearance of Edwardsiella ictaluri in the peripheral blood of channel catfish Ictalurus punctatus fingerlings were monitored for 216 h after exposure to E. ictaluri for 4 h and 8 h under static condi tions. Most fish exposed to E. ictaluri developed bacteriemia 24 h pos t-exposure, and by 72 h post-exposure E. ictaluri was recovered from a ll the blood of all exposed fish. The number of E. ictaluri colony for ming units (CFU) in the blood of moribund fish ranged between 1.7 x 10 (3) to 1.6 x 10(5) CFU/50 mu L whole blood. Clearance of bacteria from the blood was observed by 216 h post-exposure and all fish surviving bacterial exposure developed agglutinating antibody against E. ictalur i. The pathogenesis of the infection was accompanied by the shedding o f viable E. ictaluri into the mater which may serve as a mechanism by which fish to fish transmission occurs.